Field effect transistors having a movable gate structure, so-called “Moving Gate”-FETs, are suitable for detecting small movements. They generally have a very good signal-to-noise ratio and can therefore be used, for example, as acceleration sensors in miniaturized sensor cores in the field of inertial sensor technology.
Field effect transistors having a movable gate structure have a substrate, in which an n-doped or p-doped channel is introduced between a drain region and a source region. An insulation layer is applied above the channel region, a gate structure in turn being arranged above said insulation layer. In this case, the gate structure is configured in a movable fashion, that is to say that an external force acting on the gate structure can deflect the gate structure in a direction perpendicular to the substrate surface and/or in a direction in the plane of the substrate surface. As a result of this deflection, when a gate voltage is present at the gate structure, the charge carrier density in the channel region changes, which in turn leads to a change in resistance between drain region and source region. This change is resistance can be measured, either by applying a constant gate voltage to the gate structure, keeping the drain-source voltage constant and measuring the current flowing through the field effect transistor or the change in current intensity caused by the deflection, or by impressing a constant current into the field effect transistor and measuring the change in the drain-source voltage on account of the deflection.
The document US 2002/0005530 A1 discloses a field effect transistor having a flexibly mounted gate electrode above a planar substrate, wherein an acceleration of the field effect transistor results in a deflection of the gate electrode relative to the substrate, as a result of which a change in the current intensity in a channel region of the field effect transistor becomes measurable.
The document EP 0 990 911 A1 discloses a micro-mechanical sensor on the basis of a field effect transistor having a movable gate, the deflections of which bring about a variation of the channel region of the field effect transistor that is overlapped by the gate.
The document WO 2010/124889 A2 discloses an analysis circuit for a field effect transistor having a movable gate, said transistor being connected in series with a reference transistor. A nonlinear measurement signal of the movable gate can be tapped off at an intermediate node between the two field effect transistors.